Structure of The Atmosphere
The Atmosphere is composed of 78 percent of Nitrogen, 21 percent oxygen and 1 percent of other gases.As some of these elements are heavy and some light, the heavy ones settle toward the surface.For this very reason that oxygen is found only to a max of 35,000 feet. Air just like any body reacts to scientific laws because it has mass and weight. Air resting upon the surface of the earth and over the ocean has pressure the average of those pressure of 14.7 pounds per square inch or 29.92 inches of mercury. The thickness of the atmosphere is limited, the higher you go less of air is found. At 18,000 feet weight of the atmosphere is half of what it is at sea level.
Atmospheric Pressure is defined as the force exerted per unit area against a surface by the weight of air above that surface at any given point in the Earths atmosphere. Weather changes are based on atmospheric pressure, lift is based on it too , and also important fight instruments. Now atmospheric pressure can effect density, as air becomes less dense it will reduce power of an aircrafts engine because of less air, thrust of an aircraft reduce due to thin air the propeller is inefficient in less and lift because thin air produces low aerodynamic forces.
Next is obviously the effects of pressure on density, but what is density? Density of any substance is mass per unit volume. Its represented as rho (the Greek letter). Now air can be expanded or compressed, when air is compressed a greater amount of can occupy a given volume. When pressure is reduced, the air expands and occupies greater space. At a constant temperature , if the pressure is doubled so will the density. Therefore, at constant temperature pressure and density are directly proportional .
The effect of increasing the temperature of a substance is to decrease its density, and if the tempereature is reduces the density increases. So therefore, density is inversly propotional to the absolute temperature at constant pressure. As you climb in the atmosphere the pressure and temperature reduce and have conflictiong effects on density. A rapid drop in pressure as altitude is increased usually has a dominating effect. Hence, density reduces as altitude is increased.
All this time we have left out one factor which occurs in reality, that is humidity. Humidity is defined as the amount of water vapour content in the atmosphere at a given place. There are various types of humidity and will be discussed later. It is important to know that moist air is lighter than dry air and it is also comparitivlly less dense. Also warm and moist air relate to light air masses and cold dry air relates to heavy air masses. Pressure, Temperature , Density and Humidity have a great influence on an aircrafts performance.
Understanding these basic terms and the structure of the atmosphere will help you understand how your aircraft behaves in various conditions. The structure of the atmosphere is a very vast, so what we are doing is giving you what is required when its required.Stayed tuned as we will be back with more only at MyAviationTutor.com
